From the vCenter Update Manager PowerCLI Release Notes:
"Update Manager PowerCLI 4.0 Update 1 works only with Update Manager 4.0 Update 1."
So I am afraid you have to upgrade first to VMware vSphere 4.0 update 1.
There has been a VMware Update Manager snap-in for an old version of the VI Toolkit. But that doesn't work with the current version of PowerCLI.
Regards, Robert